This invention relates to apparatus for mixing and dispensing multi-component fluids and more particularly, it concerns foam dispensing guns adapted to be used with resin systems in which two or more fluid components, separately stored in pressurized vessels, are mixed and dispensed as settable foam.
U.S. Pat. No. 3,399,837, issued Sept. 3, 1968 to C. E. Frick, No. 3,633,795 and No. 3,784,110, the latter two having been issued respectively on Jan. 11, 1972 and Jan. 8, 1974 to William R. Brooks, disclose dispensing guns for urethane foam and the like in which separate fluid components are fed individually to the gun, passed separately through controlled valve ports and brought into contact with each other only upon reaching a mixing chamber of a nozzle from which the mixed components are discharged as foam. In each instance, the nozzle of the gun is designed to be disposable in order to avoid the necessity for cleaning any part of the gun which comes into contact with mixed as distinguished from separate foam producing fluid components. As a result, the initial fluent characteristics of the foam producing components may be maintained without wastage even through use of the gun may be interrupted for time intervals of sufficient duration for the mixture to set in and plug the nozzle. In other words, the gun is restored to a ready-to-use condition simply by replacing a nozzle plugged by solidified or set foam.
The fluid components of the foam producing resin system used with dispensing guns exemplified by the disclosures of the aforementioned patents, are fed to the gun under pressures up to 250 psi. Because of the pressure drop at the gun nozzle, the rate of fluid component flow is easily controlled by a relatively simple trigger actuated valve arrangement. Back pressure exerted on the nozzle in use, however, requires that the replaceable nozzle be retained on the gun body with sufficient holding force to handle the pressures involved without accidental dislodgement of the nozzle from the gun. In the past, the provision of a suitably strong nozzle mount has involved compromise with avoidance of complex, expensive or cumbersome gun structure.
An additional and particularly acute problem is presented in the design of such foaming guns due to the potential for accidental discharge of the fluid components when the nozzle is not in place on the gun. During the replacement of a nozzle, for example, accidental operation of the trigger-controlled valve on the gun could result in a sudden release of both fluid components under the pressures mentioned. The occurrence of such accidental discharge presents not only a safety hazard to the operator of the gun but also a source of potential damage to previously dispensed foam and the working environment in general. While safety devices have been proposed, they have generally required positive action on the part of the gun operator to place the gun in a "safe" condition. Thus, failure of the operator to take such action will result in the gun being left in an unsafe condition where accidental discharge of the unmixed fluid components might occur.